Cystic Fibrosis (CF) is characterized by a thick dehydrated mucous film in airways, which is clinically manifest as a decrease in mucociliary clearance and respiratory function. This clinical outcome is the result of alterations in absorption and secretion of ions (primarily chloride (Cl) and sodium (Na)) and water in airway epithelia. This proposal focuses on the elevated Na absorption (ESA) observed in CF airways which significantly contributes to alterations in pulmonary function by dehydrating the mucous film lining airway lumens (1,2). Regulation of Na absorption is not completely understood in the normal or CF airway. Thus there is a need to pursue fundamental characterization of Na absorption in airway to gain insight into the etiology of the ESA observed in CF patients. ESA is inhibited by amiloride, a potent blocker of Na channels residing in other absorptive epithelia (e.g. cortical collecting tubule). This agent is being employed clinically to improve pulmonary function in CF patients with some success. Unfortunately, its beneficial effects are transient (i.e. 40 minutes) (3). Our prior work indicates that the transient effect of amiloride may be due to a compensatory autoregulatory increase in Na channel density rather than a decrease in binding efficacy of amiloride (4,5). If this alternative explanation for the transient effect of amiloride is proven, differences in administration protocols for this agent might be developed. Given the importance of Na transport in CF and the documented similarities between other absorptive epithelial Na channels and those found in airway, basic characterization of Na channels in airway will be important to develop and test protocols for optimal use of current therapies (e.g. number of doses and frequency of use) and new, more effective therapies. In this proposed research we will utilized an electrophysiological technique, fluctuation analysis to characterize Na entry in cultured human nasal and guinea pig tracheobronchial epithelia to: 1) characterize the components of Na transport (open probability, channel density, single channel current) in normal and CF epithelia 2) examine the effects of amiloride on apical Na channels of airway epithelia 3) examine the effects of other regulators of Na entry in absorptive epithelia (cAMP, calcium, cytoskeletal elements). This proposal will enable the PI to enhance understanding of the mechanisms underlying CF which will facilitate enlightened practice and lead to improved clinical outcomes for CF patients. In addition, this work will strengthen the ongoing research program at the Johns Hopkins School of Nursing by serving as a base for future projects applying a basic science approach to solving clinical nursing problems.